It has become more important to use fuels which are high in sulfur content due to the storage of relative low sulfur oil feedstocks. For example, the electrical power generating industry is turning toward coal, a known high-sulfur fuel as a feedstock. Because of the increased use of these high sulfur feedstocks, it has become more important to develop means for removing the sulfur present in the fuel. One approach has been to remove the sulfur from the flue gas obtained by burning the fuel and, thus, abate the pollution problems inherent in the use of high-sulfur fuels.
The current approaches to flue gas desulfurization are of three basic types. For example, the flue gas can be scrubbed with an alkaline scrubber which chemically reacts with SO.sub.2 in the flue gas. However, this reaction favors the formation of reaction products which are so strongly combined that there is no economical way to regenerate the starting scrubber material. Another approach has been to use catalysts to oxidize the SO.sub.2 in the flue gas to SO.sub.3 which may subsequently be used for the production of H.sub.2 SO.sub.4, for example, see British Patent 945,022, which teaches the preparation of vanadium type catalysts for use in this process. This reference also teaches that cerium oxides can be combined with vanadium in the catalyst used in this oxidation process. Finally, solid or liquid scrubber systems that adsorb or react weakly with SO.sub.2 have been used, which can be regenerated thermally or chemically.
A process for removal of SO.sub.2 from flue gas is disclosed in U.S. Ser. No. 381,369, herein incorporated by reference, which utilizes a vanadium oxide sorbent, which is subsequently regenerated by desorbing the sulfur with a reducing gas.
Another process which is of this nature utilizes copper oxide as the sorbent. However, during the regeneration of the sorbent under reducing conditions, it is difficult to prevent reduction of the oxide to the metal, which is useless as a sorbent.
In a recent article, "Selection of Metal Oxides for Removing SO.sub.2 from Flue Gas" by Lowell et al., Ind. Eng. Chem. Process Des. Develop., Vol. 10, No. 3, 1971, the use of various oxides as sorbents for sulfur dioxide present flue gases is discussed. The authors evaluate 47 different oxides and suggest a group of 15 as the most promising. This group includes cerium oxide but does not discuss its use in detail nor how to regenerate the sorbent. The article suggests that the sorbents should be regenerated thermally and does not discuss the regeneration of said sorbents under reducing conditions because of the authors' feeling that the operating cost of reducing gas was advantageous. It is thus clear that the authors did not recognize the advantage of using cerium oxide as a sorbent for SO.sub.2, especially the advantages inherent in the regeneration of the sorbent under reducing conditions to form a mixture of H.sub.2 S and SO.sub.2 which can be used conveniently as a feedstock for a Claus sulfur plant.